ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02140.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02141.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:In primary cultures of rat cerebellar granule neurons, GABA treatment (50 μM, 7 days) caused a withdrawal supersensitivity selective for the metabotropic glutamate receptors that mainly preferl‐glutamate, quisqua‐ late and, to a lesser extent, kainate. The withdrawal supersensitivity was absent when 10 μMSR‐95531 was coadministered with GABA during the treatment period, an event that suggests the GABAAreceptors primarily produced the GABA treatment effect. This was supported further by the inability of baclofen treatment to mimic completely the treatment effect of GABA. Withdrawal from 7 days of baclofen treatment only produced a slight increase in the metabotropic effect ofl‐glutamate and carbachol. In addition, in untreated neurons, baclofen had no acute effect, whereas GABA inhibited the effect ofl‐glutamate and carbachol. The inhibitory effect of GABA was reversed by SR‐95531 and was absent in neurons treated with GABA. These observations suggest the involvement of GABAAreceptors and the apparent development of tolerance to GABA, respectively. Also, dependence on GABA may have occurred; the metabotropic effects of glutamate, kainate, and quisqualate were not altered in neurons maintained with G

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02142.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Actin is a neuronal protein involved in axonal transport and nerve regeneration, both of which are known to be impaired in experimental diabetes. To determine if actin is subject to glycation, we rendered rats diabetic by injection of streptozotocin. Two or 6 weeks later brains were removed and a preparation of cytoskeletal proteins was analyzed by two‐dimensional polyacrylamide gel electrophoresis. Brains from diabetic animals contained an extra polypeptide that migrated close to actin and reacted with monoclonal antibody C4 against actin. It was also found in a preparation of soluble synaptic proteins from diabetic rat brain, indicating that it was at least partly neuronal in origin. This polypeptide could be produced by incubation of cytoskeletal proteins from brains of nondiabetic rats with glucose‐6‐phosphate in vitro. The appearance of this glycated actin in diabetic animals was prevented by administration of insulin for a period of 6 weeks. We could not detect any effect of glycation in vitro on the ability of muscle G‐actin to form F‐actin filaments and its significance for the function of actin remains to be determined. The finding that glycation of platelet‐derived actin from diabetic patients was significantly increased implies that the abnormality may also occur in clinic

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02143.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:A possible role for protein kinases in the regulation of free cytosolic Ca2+levels in nerve endings was investigated by testing the effect of several kinase inhibitors on the increase in cytosolic Ca2+(monitored with the Ca2+‐sensitive dye fura‐2) induced by depolarization with 15 or 30mMK+. The ability of various drugs to inhibit the cytosolic Ca2+response appeared to correlate with their reported mechanism of action in inhibiting protein kinases. W‐7 and trifluoperazine, drugs reported to inhibit calmodulin‐dependent events, were effective inhibitors of the increase in cytosolic Ca2+induced by high K+depolarization, as was sphingosine, a drug that inhibits protein kinase C by binding to the regulatory site, but which also inhibits calcium/calmodulin kinase. On the other hand, drugs that inhibit protein kinases by binding to the catalytic site, such as H‐7 (1m/W), staurosporine (1μM), and K252a(1μM), were ineffective. Activation of protein kinase C, which is blocked by each of these drugs, does not appear to be essential to the maintenance of elevated cytosolic Ca2+in depolarized synaptosomes. All of the drugs, including sphingosine, that functionally inhibit the depolarization‐induced elevation in cytosolic Ca2+have in common the ability to bind to calmodulin. Because the drugs that inhibit protein kinases by competing with ATP binding at the active catalytic site did not block the response in this system, we suggest that a calmodulin or a calmodulin‐like binding site participates in the regulation of Ca2+increases after

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02144.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:β‐Trace protein from pooled human CSF was purified to homogeneity. An apparent molecular mass of 23–29 kDa was determined for the polypeptide on sodium dodecyl sulfate‐polyacrylamide gel electrophoresis. Amino‐terminal sequencing of the polypeptide yielded the unique amino acid sequence APEAQVSVQPNFQQDKFLGRWFSA24. Alignment of amino acid sequences obtained from tryptic peptides with the sequence previously deduced from a cDNA clone isolated by other investigators allowed the identification of β‐trace protein as prostaglandin D synthase [prostaglandin‐H2D‐isomerase; (5Z, 13E)‐(15S)‐9α, 11 a‐epidioxy‐15‐hydroxyprosta‐5,13‐dienoate D‐isomerase; EC 5.3.99.2]. A conservative amino acid exchange (The instead of Ser) was detected at amino acid position 154 of the β‐trace polypeptide chain in the corresponding tryptic peptide. The twoN‐glycosylation sites of the polypeptide were shown to be almost quantitatively occupied by carbohydrate. Carbohydrate compositional as well as methylation analysis indicated that Asn29and Asn56bear exclusively complex‐type oligosaccharide structures (partially sialylated with α2–3‐ and/or α2–6‐linkedN‐acetylneuraminic acid) that are almost quantitatively α1‐6 fucosylated at the proximalN‐acetylglucosamine; ∼70% of these molecules contain a bisectingN‐acetylglucosamine. Agalacto structure

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02145.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:A rat neuroma cell line (B103 4C), deficient of hypoxanthine‐guanine phosphoribosyltransferase (HGPRT), was utilized as a model tissue in search for the biochemical basis of the Lesch‐Nyhan syndrome (LNS). The HGPRT‐deficient neurons exhibited the following properties: an almost complete absence of uptake of guanine and of hypoxanthine into intact cell nucleotides (0.92% and 0.69% of normal, respectively); a significant increase in the availability of 5′‐phosphoribosyl‐1‐pyrophosphate; a three‐ to fourfold acceleration of the rate of de novo nucleotide synthesis; a normal excretion of xanthine, but 15‐fold increase in the excretion of hypoxanthine into the culture media; a normal cellular purine nucleotide content, including the absence of 5‐amino‐4‐imidazole carboxamide nucleotides (Z‐nucleotides), but enhanced turnover of adenine nucleotides (loss of 86% of the radioactivity of the prelabeled pool in 24 h, in comparison to 73% in the normal line), and an elevated UTP content. The results suggest that, under physiological conditions, guanine salvage does not occur in the normal neurons, but that hypoxanthine salvage is of great importance in the homeostasis of the adenine nucleotide pool. The finding of the normal profile of purine nucleotides in the HGPRT‐deficient neurons indicates that the lack of hypoxanthine salvage is adequately compensated by the enhanced de novo nucleotide synthesis. These results did not furnish evidence in support of the possibility that GTP or ATP depletion, or Z‐nucleotide accumulation, occurs in HGPRT‐deficient neurons and that these are etiological factors causing the neurological abnormalities in LNS. On the other hand, the results point to the possibility that elevated hypoxanthine concentration in the brain may have an etiological

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02146.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:We have investigated the synthesis, axonal transport, and processing of the β‐amyloid precursor protein (APP) in in vivo rabbit retinal ganglion cells. These CNS neurons connect the retina to the brain via axons that comprise the optic nerve. APP is synthesized in retinal ganglion cells and is rapidly transported into the optic nerve in small transport vesicles. It is then transferred to the axonal plasma membrane, as well as to the nerve terminals and metabolized with a f1/2of less than 5 h. A significant accumulation of C‐terminal amyloidogenic or nonamyloidogenic fragments is seen in the optic nerve 5 h after [35S]‐ methionine, [35S]cysteine injection, which disappears by 24 h. The major molecular mass species of APP in the optic nerve is ∼110 kDa, and is an APP isoform that does not contain a Kunitz protease inhibitor domain. Higher molecular mass species containing this sequence are seen mostly in the retina. A protease(s) that can potentially cleave APP to generate an amyloidogenic fragment is present in the same optic nerve membrane compartmen

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02147.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Slices from human neocortex preincubated with [3H]serotonin ([3H]5‐HT) were superfused and stimulated electrically to investigate whether the α2‐adrenoceptors on serotonergic terminals can be stimulated by endogenous noradrenaline (NA) released from neighboring noradrenergic fibers. The stimulation‐evoked3H overflow, representing action potential‐induced, exocytotic release of 5‐HT, was depressed by the NA uptake blocker (+)‐oxaprotiline. Rauwolscine (a mixed α2‐adrenoceptor antagonist/5‐HT autoreceptor agonist) or phentolamine [a combined α‐ adrenoceptor/5‐HT autoreceptor antagonist; the latter drug in the presence of (+)‐oxaprotiline] enhanced the release when the 5‐HT autoreceptors had previously been blocked by metitepine. Under hypothermia the release of 5‐HT was found to be decreased and that of NA to be increased; under these conditions idazoxan (an α2‐adrenoceptor antagonist) enhanced the release of 5‐HT. In neocortex slices from rats (+)‐oxaprotiline similarly depressed the release of 5‐HT (measured with the same methods) as in human tissue. When rats were pretreated with 6‐hydroxydopamine, the inhibitory effect of exogenous NA on 5‐HT release was increased, and in slices from rats pretreated with desipramine, it was decreased. In conclusion, α2‐heteroreceptors can be activated by endogenous NA released from neighboring noradrenergic fibers. Because regulatory processes analogous to those in rats probably occur in humans as well, an up‐ or down‐regulation of α2‐ heteroreceptors in depressed patients with a (pathological) decrease or a (therapeutic) enhancement of the noradrene

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02148.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:A single dose of x‐irradiation was applied on the cephalic end of newborn rats, and the alterations in the noradrenergic afferents to the cerebellum were studied 180 days later. A net increase in the noradrenaline content of cerebellum was found (122% of nonirradiated controls). The response of noradrenaline content to reserpine injection (0.9 mg/kg, i.p.) was similar in exposed and control rats. Likewise, the3H release induced by Ro 4‐1284 from cerebellar cortex slices labeled with [3H]noradrenaline was unmodified by x‐rays, although a mild increase in the spontaneous efflux of3H was found. The retention of3H by the slices was reduced in exposed animals (58% of controls). Both the in vitro activity of tyrosine hydroxylase and the accumulation of L‐3,4‐dihydroxyphenylalanine (L‐DOPA) were not significantly different between x‐treated rats and controls. In contrast, monoamine oxidase activity was markedly reduced in x‐irradiated cerebellum (38% of controls). The x‐ray‐induced decrease in cerebellar weight (—60%) resulted in marked increases in noradrenaline concentration (223%), tyrosine hydroxylase activity per milligram of protein (206%), and3H retention (50%). The accumulation of L‐DOPA per gram of tissue was also increased at every time considered. These data indicate that x‐irradiation at birth produces a cerebellar loss not completely shared by the noradrenergic afferents, and a permanent imbalance between the noradrenergic afferent input and its target cells might eventually result. In spite of the enhanced noradrenaline content, the lack of increase in maximal tyrosine hydroxylase activity and3H retention seems to indicate that a long‐term sprouting of the noradrenergic terminals in the cerebellum induced by the ion

ISSN:0022-3042    

DOI:10.1111/j.1471-4159.1993.tb02149.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY